3D modeling of gas hydrates distribution in South Hydrate Ridge (Cascadia accretionary prism, offshore Oregon) through geological time

Abstract

South Hydrate Ridge (SHR) is an anticlinal structure that is part of the Cascadia accretionary prism, located offshore of Oregon. SHR has been the subject of multiple multidisciplinary studies and oceanographic campaigns focused on understanding the functioning of gas hydrate systems. Herein, we present a 3D dynamic model of SHR that simulates the distribution of gas hydrates over geological time. This model is based on the application on petroleum system modeling tools and builds upon previously published data and results from 2D models already published. The model reproduces the complex structure of SHR and distinguishes a total of 7 stratigraphic units (from the Pliocene to the Present), primarily composed of silty clays and clays interbedded with sands. The model predicts a heterogeneous distribution of gas hydrate saturation in SHR at present, with higher values observed on the flanks of the main ridge and on the crests of secondary highs (maximum values of up to 23% of porosity). According to the model, the initiation of hydrate formation occurred mainly between 1.7 Ma and 1.6 Ma, and its accumulation has persisted throughout the evolution of the ridge, alternating with dissociation in certain areas and moments. Such variable distribution and the alternation of formation and dissociation would respond to the differential growth of the structures forming the SHR. These structures control the availability of gas, which migrates upward through deformed strata, and would influence the distribution of the gas hydrate stability zone.